[What's up with my Dojo's skin rotting]

Thanks everyone. Cory in thuus 90 gal tank are 3 Dojos, 1 Blue Acara Male,  the Synodontis catfish,  a Royal pleco,  3 SAE's. 4 Red Hook Silver Dollars. Temp in tank is 75, will certainly follow advice.  

[What's up with my Dojo's skin rotting]

2 hours ago, Cory said:

First thing I would do is fix the ph and nitrates. Get the pH up to 7.0-7.2 and nitrate to 50ppm or lower. Then I would have 1 dose of maracyn in the tank for a week. What is the water temperature? Anything about 76 is likely to be causing some stress. I'd try to keep it around 72-74 for the dojo loaches. 

What else is in there besides the dojos and the synodontis catfish? it looks like it's dorsal fin has been nipped, if there is aggression there, that is another further stress factor. Think of you having a bad injury and trying to heal, but being in a dirty environment, it being too hot, and the wrong pH. All those factors tax the body and don't allow it the resources to fight the bacterial infections.

 

[What's up with my Dojo's skin rotting]

https://s.amsu.ng/EQLm3kLVauzN

Poor thing started with it looking like he had scratched himself maybe on wood while swimming,  but the fishes and the wood have all been in there for over 2 years.  We had another Dojo same type, bought together over 2 years ago, that got this and we treated with Erythromycin but he died. Now a few months later this guy has it.  Please help.  We have been treating this time with Maracyn we got from AC. Water test shows GH is 120, KH is 40, pH is  6.5, No2 is  .5, No3 is 160. Please help,  I can't stand how bad this must hurt him, btw, he's still eating and swimming but not with his normal high activity.